Glad to hear everything's back to normal.
Doesn't really matter what your next protein is--may as well go with something which, like chicken, is readily available and will hopefully be a regular part of the diet.
Some options include turkey or pork--or any kind of fish. Beef is great too, but I have a hard time finding any cut of beef that isn't outside my price range for dog food. Beef heart is usually cheapest. Venison is available to many folks, so that could be an option too.
Most of us will sometimes add in new things every now and then just as a way to add variety, but they aren't items that the dogs get too often. Lamb, mutton, rabbit, goat, quail, emu--you name it. But I don't see any reason to try any of these things early on in the diet. You may as well get through all the "staple" proteins first.
Other stuff like eggs and oils can be worked into your one-thing-at-a-time protocol too.